Transient hypogammaglobulinemia of infancy is characterized as a reduction of one or more classes of immunoglobulins with a response to vaccines and normal subpopulations of lymphocytes B presenting in the first years of life. The diagnosis is made a posteriori, once the levels of immunoglobulins are normalized, in general between 2 and 4 years of age. Clinical presentation varies : the child may be either asymptomatic or present with recurrent infections, atopy and / or auto-immunity. There are no clinical or immunological features that distinguish this condition from a common variable immunodeficiency (CVID). Because of the risk of severe infections, it is necessary a follow up by a paediatric immunologist. Depending on the presentation and evolution, a prophylaxis with antibiotics or a substitution with immunoglobulins might be indicated.